1. Field of the Invention
The present invention relates to a light beam heating apparatus to be used as a local non-contact heating source for soldering electronic components.
2. Description of Related Art
FIG. 2 shows an optical system structure of a conventional light beam heating apparatus.
The principle of the light beam heating apparatus is described below. A bright point of a light source 1 and an incident edge face of a bundled optical fiber 3 are disposed on the first and second focal points of a condensing mirror 2, respectively. A light beam irradiated from the light source 1 is condensed on the second focal point by the condensing mirror 2 and enters the bundled optical fiber 3. The light beam, entered into the bundled optical fiber 3, is transmitted through the optical fiber and irradiated from an irradiation edge face. The light beam irradiated from the irradiation edge face is condensed, by a condensing lens mechanism 4, into a light beam having a predetermined diameter and reaching a light irradiated section 5.
With regard to the condensing lens mechanism, FIG. 3 shows the construction of a conventional condensing lens. As shown in FIG. 3, the conventional condensing lens is constructed with a single aspherical lens 6. The aspherical lens 6 is designed to condense light in the most preferable manner for a predeteremined wavelength of light and beam magnification (diameter of a condensed beam/diameter of a bundled optical fiber).
However, the conventional condensing lens mechanism 4 has a problem of declining imaging capacity caused by increasing lateral aberration which occurs with changes in the wavelength of light and beam magnification. Furthermore, when the wavelength of the light irradiated from the light source 1 is relatively wide, as is the case with xenon light, deviation in imaging position occurs due to chromatic aberration. These problems cause dispersion of the energy depending on the wavelength, leading to a failure of the condensed beam to form an image clearly, and resulting in lower energy concentration at the light condensing section.
The construction, which includes a single aspherical lens 6, has difficulty condensing light while suppressing lateral and chromatic aberration at each magnification.
The present invention aims to provide a construction of a condensing lens which solves the foregoing problems.